My 14 year old just took her first plane trip to NH from PA. It's usually a 12 hour drive, and she goes with family members. They make the trip every summer. I've always been nervous to have her fly as she is sensitive to a host of things, sounds, sensations. She may scream in response. Not a good thing on a plane these days. So, we spent time preparing, and talking about the things she would see, how she would stand in line, that there would be noise of people talking, flights being announced. We talked about the light woosh sound in the background on the plane, what the bathrooms are like, what it felt like and sounded like when the plane takes off and lands. We talked about what turbulence feels like and that it's normal. Any detail we could think of. We also looked on Google for sites about first time flying. There is an article on this site about how one woman handles flying, http://williamstillman.com/ just click on articles. We also talked about things like, how when you go through the security checkpoints, sometimes it feels invasive, but it's for everyone's safety, and everyone has to do it.
My daughter just arrived back home tonight and she LOVED flying. She can't wait to do it again, and she had absolutely no problems. She said the only thing she wasn't prepared for was the annoying voice of one flight attendant. She's sensitive to voices, different tones and types. But it was all wonderful for her
I was so relieved!!
Now I don't know if she could have handled it alone. That's another issue. She was comfortable with family there with her. You might think about just visiting an airport with a friend, and see what it's really like, if you haven't.
Hope this has been helpful 
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Bunni
That which doesn't kill me, makes me stronger, and really pisses me off.